A good salesman and farmer's daughter joke

{ed Reportedly by John Valby}
A salesman is driving down a country road one day when his car broke down.
There was a farm near by, so he went up to ask for some help. The farmer
suggested that his daughter, Nelly, could give him a ride into town to get
the necessary parts for his car. Nelly was an innocent girl, the epitome of
virginal beauty.
Nelly and the salesman were on their way into town when he convinced her to
pull over to the side of the road to enlighten her about the facts of life.
They had some down and dirty sex all over the car, and then went into town
to get the car parts. By the time they got into town, the auto store was
closed, so they had to return to the farm. The farmer allowed the salesman to
spend the night in the barn and get his car fixed in the morning.
The next morning the salesman went up to the farmhouse to get Nelly so she
could give him a ride into town. Nelly was gone, however, and her sister
Venus opened the door. Venus was very unlike Nelly. She was sexy, voluptuous,
and really even a bit sleazy. Venus volunteered to give the salesman a ride
into town, and off they went. Venus did the convincing this time, and the
salesman had the "ride" of his life. They eventually made it back to the farm
with the parts, and the salesman fixed his car. He thanked the farmer, left
his address to they could keep in touch in the future, and went on his merry
way.
A few months later the salesman received a later from the farmer which
contained only a poem:
Were you the one who did the pushin'
Left the bloodstains on the cushion
And the footprints on the dashboard upside down?
'Cause since you met my daughter Nelly,
There's a swelling in her belly,
And you'd better get your ass back into town.
The salesman thought for a minute, and wrote the following response:
Yes, I was the one who did the pushin'
Left the bloodstains on the cushion
And the footprints on the dashboard upside down.
But since I met your daughter Venus,
I've had some problems with my penis,
So I guess we're pretty even all around.